1. Field of the Invention
The field of the invention relates to a means for accurately guiding flexible magnetic recording tape within a data cartridge. The invention is particularly applicable to precision magnetic recording cassettes where said cassettes are intended for head alignment purposes and/or other critical recording applications.
2. Description of the Prior Art
Many techniques have been employed over the years to accurately position magnetic recording tape with respect to a magnetic recording read/write transducer or head. Stationary posts, rollers of various geometries with and without flanges, and blasts of air have all been used to guide magnetic recording tape. The object of all of the techniques has been to position the magnetic medium in space so that the reading and writing of information may be performed reliably, i.e. without error. Reliable retrieval of information from magnetic media is very difficult, if not impossible, if the magnetic recording gap of the head is not precisely located with respect to information which is desired to be read. By far the most common and least expensive way of guiding magnetic recording tape has been by a combination of stationary guides used in conjunction with rollers carefully positioned within the tape path to achieve the desired tracking accuracy.
U.S. Pat. No. 3,263,936 to Williams discloses a tape cassette utilizing two hubs or flanged spools located coaxially within a housing wherein posts or guides fixedly mounted to a transparent cover guide the tape from one spool hub to the other. Because of the configuration of the tape cassette, a change in the plane of motion of the tape is required, and said posts or guides achieve said change in plane. The posts or stationary guides are formed and/or shaped to properly track the tape from the plane of one hub or spool to the other, but the invention does not teach or even suggest how extreme tracking accuracy in the area of the magnetic head can be achieved.
U.S. Pat. No. 3,744,696 to Warren teaches the use of a guide apparatus for controlling the contact of a magnetic recording medium or web with the periphery of a pinch roller. In order to reduce the contact wrap of the magnetic medium with the pinch roller, a guide mechanism lifts the magnetic medium off the pinch roller. While Warren recognizes the need for accurate control of the position of the magnetic medium, the application of guides to magnetic tape in a cassette environment or the application of guides to critically control the positioning of the tape in the area of the magnetic recording head is not taught or even suggested.
U.S. Pat. No. 3,831,882 to Fitterer et al discloses the use of stationary guides to magnetic recording cassettes to control the path of the tape coming from a flangeless spool and crossing a roller prior to contact with a magnetic recording head. By its structure, considerable vertical tolerance variation on the position of the flangeless spools within the tape cassette occurs. Uncontrolled variation of the height of said spools within the cassette causes degradation in the reliability of the magnetic recording cassette. Compensation for said spool height variation is attempted by guiding the tape in its path from the flangeless spool to the edge roller of the cassette. The problem of edge roller vertical motion is not addressed, and while the invention does somewhat improve the tracking accuracy and repeatability of the position of the tape in space within the cassette, the guiding of the magnetic recording tape within the area of the magnetic recording head after the edge roller is not taught or suggested.
U.S. Pat. No. 3,991,956 to Machida suggests use of stationary guides to control the position of the magnetic recording tape within a tape cassette. However, like Fitterer et al as discussed above, Machida teaches the guiding of the tape between the reel and the edge roller. Such guiding is necessitated by allowable tolerances within the cassette permitting the vertical position of the reels within the cassette to significantly vary. As the most critical position of the tape within the cassette is its relationship to the magnetic recording head during reading and/or writing, neither Fitterer et al nor Machida teach guiding of the magnetic recording medium in an area other than between the take-up or supply reels and the edge rollers. Neither teach or even suggest addressing the guiding problem in the area where it is most critical, i.e. between the edge rollers in the area of the magnetic recording head.